High current electrostatic generator



Oct. 28, 1958 A. J. GALE I HIGH CURRENT ELECTROSTATIC GENERATOR Filed Aug. 16,1957

' 2,858,501 HIGH CURRENT ELECTROSTATIC GENERATOR Alfred J. Gale, Lexington, Mass, assignor to High VoltageEngineering .Corporation, Burlington, Mass, a corporation of Massachusetts Application August 16, 1957, Serial No. 678,564 Claims. (Cl. 322-2) This invention relates to belt-type electrostatic generators and in particular to a low-voltage belt-type electrostatic generator capable of delivering high currents. In a co-pending application assigned to the assignee of the present invention there is disclosed and claimed a compact neutron source which is driven by a pair of electrostatic generators. One of these electrostatic generators delivers a relatively high voltage for the purpose of accelerating positive ions against a target for the production of neutrons. The other electrostatic generator generates a relatively low voltage for the production of ions. While the current associated with the high voltage generator is approximately equal to the current in the ion beam and is relatively low, the current delivered by the smaller genorator must be greater than the current in the accelerated beam and must be approximately equal to the current in the discharge in the ion source. Accordingly, one application of the present invention is its use as the ionsource voltage generator for such a neutron source. However, the invention is not limited to this application but includes any application where relatively high currents at low voltages are desired.

The invention may best be understood from the following detailed description thereof having reference to the accompanying drawing in which:

Fig. 1 is a diagrammatic view of a belt-type electrostatic generator embodying the invention; and

Fig. 2 is a diagrammatic view of a belt-type electrostatic generator in the high voltage terminal of which there is provided a high current electrostatic generator embodying the invention.

Electrostatic generators are well known and are disclosed for example, in United States Patent No. 1,991,236 to Van de Graatf and No. 2,252,668 to Trump and at vol. XI, page 1 of Reports on Progress in Physics (1948). These devices generate high voltage by carrying electric charge to a hollow electrode on an insulating belt. The belt is generally supported on two pulleys, one of which lies within the hollow electrode and the other of which is at ground potential. The charge is usually deposited on the belt at the grounded end thereof by means of a corona discharge between a set of sharp points and the grounded pulley. The charge is removed from the belt by another set of corona points within and electrically connected to the hollow electrode. Thehollow electrode acts as a Faraday cage, so that the charge on the belt is readily picked up by the points. However, in low-voltage applications the electric fields are localized, and the hollow electrode may often be eliminated.

Referring to the drawing, and first to Fig. 1 thereof. the electrostatic generator therein shown diagrammatically includes a first pulley 1, a second pulley 2 and an an endless belt 3, each of insulating material. These insulating materials are so chosen with respect to their position in the triboelectric series that the first pulley 1 tends to become positive and the second pulley 2 negative with respect to the belt 3. A first set of corona points 4 is positioned near the first pulley 1 and is connected to the atn t" Q 2. local ground through a first resistor 5. Upon rotation of the pulleys 1, 2, the resultant interaction between the surfaces of the first pulley 1 and the belt 3 produces an accumulation of positive charge on the first pulley 1, by virtue of which a corona discharge is initiated from the points 4 which deposits negative charge on the belt 3. The belt 3 continually carries this negative charge away, and as a result, negative current flows from the local ground through the first resistor 5, thereby raising the potential of the first set of corona points 4 to a positive voltage with respect to the local ground. The first set of points 4 is electrically connected by leads 6 to a series of inductor plates 7 positioned close to and spaced along the up-run of the belt 3. A series of sets of corona points 8 are positioned similarly on the opposite side of the uprun of the belt 3 and are connected to the local ground. Since these points 8 are at negative potential with respect to the inductor plates 7, the resultant corona discharge therebetween deposits additional negative charge onto the belt 3. Between adjacent pairs of points 8 and inductor plates 7 a corresponding series of sets of collector points 9 are positioned so as to remove the negative charge deposited on the belt 3 by the preceding set of spray points 4, 8. The collector points 9 are all connected together and joined to a common terminal 10 at which the negative charge is accumulated. The effect of the up-run of the belt 3, then, is to carry a large quantity of negative charge a relatively short distance; and all this negative charge is accumulated at the negative terminal 10.

The apparatus which has just been described produces a negative voltage at the negative terminal 10 with respect to the local ground, and the potential difference thus established may be used as a voltage source capable of delivering a relatively high current. The local ground referred to may be the conventional ground, as this term is usually understood, or it may refer to the potential of certain parts of a larger apparatus. For example, the electrostatic generator of the invention may be used as a voltage source within the hollow electrode of, a larger electrostatic generator. Thus, referring to Fig. 2, the local ground comprises the high voltage electrode 11 of an electrostatic generator 12, and a high current elect-rostatic generator 13 constructed in accordance with the invention is positioned within the high voltage electrode 11 as shown.

An arrangement similar to that hereinbefore described may be provided to utilize the down-run of the belt for carrying positive charge to a positive terminal. Thus, referring again to Fig. 1, a second set of corona points 14 is positioned near the second pulley 2 and is connected to the local ground through a second resistor 15. Movement of the belt 3 over the upper pulley 2 produces an accumulation of negative charge on the second pulley 2, by virtue of which a corona discharge is initiated from the points 14 which deposits a positive charge on the belt 3. The resultant positive current which flows from the local ground through the second resistor 15 raises the potential of the second set of corona points 14, together with that of a second series of inductor plates 16, to a negative voltage with respect to the local ground. The resultant corona discharge from a second series of sets of corona points 17 deposits additional positive charge onto the belt 3. The positive charge so deposited on the belt 3 is removed by a second series of sets of collector points 18. The collector points 18 are all connected together and joined to a common terminal 19 at which the positive charge is accumulated. The eitect of the device is to cause a relatively small potential diiference to appear between the negative terminal 10 and the positive terminal 19, but the device is capable of driving a load which absorbs a relatively large amount of current.

Having thus described the principle of the invention together with illustrative examples of apparatus embodying the invention,'it is to be understood that although specific terms are employed, they are used in a generic and descriptive sense and not for purposes of limitation, the scope of the invention being set forth in the following claims:

I claim:

1. A high current belt-type electrostatic generator comprising in combination an endless belt of insulating material supported upon a first pulley and a second pulley, at least said first pulley being of insulating material so related in the triboelectric series to the insulating mate rial of which said belt is composed that an electric charge of one sign is built up on said first pulley as said belt moves over said first pulley; means for imparting traveling movement to said belt; at least one spray point connected to local ground through a resistive path and adapted to spray electric charge of the opposite sign onto the outer surface of said belt as a result of the electric field produced by the electric charge accumulated on said first pulley; at least one series of collector points arranged in spaced relationship along that run of the belt which moves away from said first pulley and in close proximity to said belt, at least one series of spray points alternating with said collector points; a series of inductor plates corresponding to said series of spray points and placed opposite thereto so as to flank said belt; and means for causing the voltage drop across said resistive path to produce a voltage difference between said spray points and said inductor plates.

2. A high current belt-type electrostatic generator comprising in combination an endless belt of insulating material supported upon a first pulley and a second pulley, at least said first pulley being of insulating material so related in the triboelectric series to the insulating material of which said belt is composed that an electric charge of one sign is built up on said first pulley as said belt moves over said first pulley; means for imparting traveling movement to said belt; at least one spray point connected to local ground through a resistive path and adapted to spray electric charge of the opposite sign onto the outer surface of said belt as a result of the electric field produced by the electric charge accumulated on said first pulley; at least one series of collector points arranged in spaced relationship along that run of the belt which moves away from said first pulley and in close proximity to said belt, said collector points being connected to a common terminal to which electric charge of said opposite sign is delivered; at least one series of spray points alternating with said collector points and connected to said local ground; a series of inductor plates corresponding to said series of spray points and placed opposite thereto so as to flank said belt; and means for causing the voltage drop across said resistive path to produce a voltage ditference between said spray points and said inductor plates of such polarity that said spray points are adapted to spray electric charge of said opposite sign onto said belt.

3. Electrostatic apparatus comprising a belt-type electrostatic generator having a hollow electrode at high voltage which encloses a second electrostatic generator in accordance with claim 2, said hollow electrode comprising said local ground.

4. A high current belt-type electrostatic generator comprising in combination an endless belt of insulating material supported upon a first pulley and a second pulley, at least said first pulley being of insulating material so related in the triboelectric series to the insulating material of which said belt is composed that an electric charge of one sign is built up on said first pulley as said belt moves over said first pulley; means for imparting traveling movement to said belt; at least one spray point connected to local ground through a resistive path and adapted to spray electric charge of the opposite sign onto the outer surface of said belt as a result of the electric field produced by the electric charge accumulated on said first pulley; at least one series of collector points arranged in spaced relationship along that run of the belt which moves away from said first pulley and in close proximity to said beit, at least one series of spray points alternating with said collector points; and a series of inductor plates corresponding to said series of spray points and placed opposite thereto so as to flank said belt; said series of inductor plates and said series of spray points being connected in parallel across said resistive path.

5. A high current belt-type electrostatic generator comprising in combination an endless belt of insulating material supported upon a first pulley and a second pulley, said pulleys being of insulating material so related in the triboelectric series to the insulating material of which said belt is composed that a positive electric charge of one sign is built up on said first pulley as said belt moves over said first pulley and a negative electric charge is built up on said second pulley as said belt moves over said second pulley; means for imparting traveling movement to said belt; at least one negative spray point connected to local ground through a first resistive path and adapted to spray negative electric charge onto the outer surface of said belt as a result of the electric field produced by the electric charge accumulated on said first pulley; at least one positive-spray point connected to local ground through a second resistive path and adapted to spray positive electric charge onto the outer surface of said belt as a result of the electric field produced by the electric charge accumulated on said second pulley; at least one series of negative-collector points arranged in spaced relationship along that run of the belt which moves away from said first pulley and in close proximity to said belt, at least one series of negative-spray points alternating with said negative-collector points; a first series of inductor plates corresponding to said series of negative-spray points and placed opposite thereto so as to flank said belt; means for causing the voltage drop across said first resistive path to produce a negative voltage at said negative-spray points with respect to said first series of inductor plates; at least one series of positive-collector points arranged in spaced relationship along that run of the belt which moves away from said second pulley and in close proximity to said belt; at least one series of positive-spray points alternating with said negative-collector points; a second series of inductor plates corresponding to said series of negative-spray points and placed opposite thereto so as to flank said belt; and means for causing the voltage drop across said second resistive path to produce a positive voltage at said positive-spray points with respect to said second series of induct-or plates.

No references cited. 

